Collector/building/... : links to specific authenticators are invalid

[chalin]

Links to specific authenticators are invalid, for example:

opentelemetry.io/content/en/docs/collector/building/authenticator-extension.md

Lines 35 to 37 in 6793481

	- [go.opentelemetry.io/collector/config/configauth/ServerAuthenticator](https://pkg.go.dev/go.opentelemetry.io/collector/config/configauth#ServerAuthenticator)
	- [go.opentelemetry.io/collector/config/configauth/GRPCClientAuthenticator](https://pkg.go.dev/go.opentelemetry.io/collector/config/configauth#GRPCClientAuthenticator)
	- [go.opentelemetry.io/collector/config/configauth/HTTPClientAuthenticator](https://pkg.go.dev/go.opentelemetry.io/collector/config/configauth#HTTPClientAuthenticator)

The following PR might help us address this issue, by providing us with anchors to (at least) the server- and client-authenticator sections:

• [editorial] Add headings to configauth/README.md opentelemetry-collector#12309